Field of the Invention
The present invention relates to an X-ray analyzing apparatus which corrects so-called peak shift.
Description of Related Art
In a conventional wavelength dispersive X-ray fluorescence spectrometer, a sample is irradiated with primary X-rays, a spectroscopic device monochromates fluorescent X-rays generated from the sample, a detector detects the monochromated fluorescent X-rays to generate pulses. A voltage of the pulse, that is, a pulse height corresponds to energy of the fluorescent X-rays, and specifically, is considered to be proportional to the energy. The number of pulses per unit time corresponds to intensity of the fluorescent X-rays. Thus, among the pulses, pulses in a predetermined voltage range (defined by an upper limit value and a lower limit value, and called “window”) are selected by a pulse height analyzer, and a counting rate (number of pulses per unit time) of the pulses is obtained, as an X-ray intensity, by a counting unit such as a scaler.
However, it has been known that, for example, in a case where a proportional counter is used as the detector, when high-intensity fluorescent X-rays are incident on the detector, a pulse voltage, that is, a pulse height to be sent to the pulse height analyzer may be suddenly lowered by several tens percent in a several seconds, and further, may be unstable within a range of approximately several percent for next ten and several minutes. This phenomenon is called peak shift, pulse height drift, or the like. When peak shift occurs, measurement is performed using an inappropriately set window which is shifted from a target wavelength, and thus, accurate analysis is impossible (see Patent Documents 1 to 4). This problem may also occur in X-ray analyzing apparatuses other than wavelength dispersive X-ray fluorescence spectrometers, and may also occur, which varies in degree, when detectors other than proportional counters are used (see Patent Documents 3 and 4).
Accordingly, as a first conventional technology for correcting peak shift, there is an apparatus that estimates a peak position (a pulse height of a target peak which is an upward projected peak in an X-ray energy spectrum to be analyzed, and more specifically, a pulse height at a vertex of the target peak) on the basis of an X-ray intensity obtained in preliminary measurement, and that changes, in main measurement, a gain of pulses from the detector such that the estimated peak position matches a reference position (an expected pulse height) corresponding to an original pulse height (see Patent Documents 1 and 2). Here, a relationship between the X-ray intensity and a lowered and stabilized peak position in the energy spectrum is obtained in advance through an experiment. In addition, as a second conventional technology for correcting peak shift, there is an apparatus that detects the peak position within a predetermined energy range including the reference position, and that dynamically (in real time) changes the gain of pulses from the detector such that the detected peak position matches the reference position (see Patent Documents 3 and 4).